It is well known in the art that the presence of certain gases in a confined space can result in serious problems to individuals or create an environment where the gases could cause an explosion. For example, it is known that problems arise in attempting to confine hydrogen and oxygen under pressure such as in electrochemical cells. In flashlights when a cell is inserted with other cells but in a reverse condition, hydrogen gas could be formed from the charging of the reversed cells by the other cells. In this situation, the hydrogen developed would be confined to the flashlight casing along with oxygen and could result in an explosion. In a similar manner, cells subjected to other abuse conditions could develop hydrogen gas buildup within the cell and thus create a hazardous situation. Other sources of hazardous gas buildup within a confined space could result in injury to human life and possibly create an explosive condition. For example, methane buildup in a mine shaft could not only injure human life but could explode thereby creating physical damage within the mine shaft.
To protect against undesirable hydrogen gas buildup in electrochemical cells, U.S. Pat. No. 3,939,006 discloses the use of a hydrogen absorbing device, preferably a discrete shaped body containing a material that will react chemically with hydrogen gas and a catalyst for the hydrogen consuming reaction. Preferably, the discrete shaped body can be encased in an electrolyte impermeable but hydrogen gas permeable membrane. The material that can react with hydrogen gas is disclosed as any solid compound which will react with or oxidize hydrogen to yield a solid or liquid reaction product. Specifically, suitable materials are those which, at ordinary ambient temperature, will exhibit a negative free energy change (.DELTA.F) associated with the reaction of that material with hydrogen. Preferred reactants include manganese oxides such as manganese dioxide (MnO.sub.2), manganic oxide (Mn.sub.2 O.sub.3), manganese hydroxide (MnOOH) and hausmannite (Mn.sub.3 O.sub.4), cupric oxide, silver oxide, mercuric oxide, manganese phosphate, bismuth trioxide, m-dinitrobenzene and quinone. Of these, manganese dioxide is particularly preferred since it is a relatively inexpensive and readily available material, and its properties and predictability in battery systems are well established.
U.S. Pat. Nos. 3,630,778 and 3,929,422 disclose a catalytic device for use in electrochemical cells in which the catalytic device comprises a foraminous body which includes exposed catalytic surfaces of relatively low gas recombining capacity and an inner nucleus of enclosed catalytic material. The nucleus comprises enclosed catalytic surfaces on which gases passing through the foraminous body react initially within a thermally favorable environment whereby cumulative heating can take place. A resulting build-up of heat at the nucleus is released to raise the temperature of the exposed catalytic surfaces to temperatures at which gases coming into contact with the exposed catalytic surfaces will start to recombine thereon, and continue to react in a sustained manner within a limited temperature range. When, as may occur, the exposed catalytic surfaces are subjected to increasing gas pressure in the battery they become self-limiting in the extent to which their temperature may be raised by exothermic reaction. Thus, the rate of recombination of gases at catalytic surfaces is controlled and limited to positively prevent the exposed catalyst surfaces from reaching temperatures at which an explosion may take place, i.e., temperatures found to be within upper limits of from about 400.degree. C. up to about 600.degree. C., and the range of control may be extended downwardly to values as low as 250.degree. C. for some battery operations. Water resulting from the controlled recombinations at the catalyst surface is returned to the electrolyte with catalyst, surfaces being maintained in a constantly reactive condition.
U.S. Pat. No. 3,817,717 discloses a hydrogen-oxygen recombining device for use in secondary batteries comprising a catalytic mass and an enclosure body having the catalytic mass totally enclosed therewithin. The catalytic mass includes a refractory substrate and a predetermined quantity of catalytic material distributed on the substrate. The enclosure body consists solely of plastic hydrophobic material and has a portion which is gas permeable. The hydrophobic material, including its permeable portion, prevents liquid and mist from the battery electrolyte from entering the body and contaminating the catalytic mass. The permeable portion permits hydrogen and oxygen to enter the body and contact the catalytic mass. The permeable portion also permits water vapor formed by recombining the hydrogen and oxygen to diffuse from the body. The catalytic mass has a catalytic metal content equivalent to a palladium content of not more than 0.1% by weight of the substrate. The catalytic mass, when inducing an exothermic reaction to recombine the hydrogen and oxygen, being characterized by a limited temperature rise within limits below that temperature at which hydrophobicity and permeability of the enclosure body would be changed.
U.S. Pat. No. 3,930,890 discloses a lightweight catalyst body bearing a finely divided metal of the platinum group encased in a porous polytetrafluoroethylene shell which is impermeable to the electrolyte of a cell because of its hydrophobic surface properties. Several small bodies of this kind, each containing about 1 milligram of palladium are inserted in each of a vehicle storage battery and float on the electrolyte surface. They not only recombine hydrogen and oxygen to water and return the water to the electrolyte efficiently, even at high ambient temperatures, but the efficiency of the catalyst is not reduced under conditions causing considerable generation of stibine. The core material on which the catalyst is provided, with or without an additional carrier, may be activated charcoal, hollow glass spheres, a porous ceramic or a synthetic resin foam. The porous hydrophobic shell may be sintered or unsintered or may be made of superimposed sintered and unsintered layers.
German Patent No. 3,503,018 discloses a battery having a plurality of cells with a recombination unit for a catalytic recombination of hydrogen and oxygen and each recombination unit has temperature sensitive sensors connected to a common line to indicate when an excessive recombiner temperature is reached.